Copolymers of poly(vinyl trifluoroacetate) or poly(vinyl alcohol)

ABSTRACT

Novel, non-crosslinked copolymers of vinyl trifluoroacetate (VTA) and up to 5 weight percent of the VTA of certain comonomers, such as vinyl esters or disubstituted ethylene monomers, are disclosed. Solvoylsis of these copolymers provides novel water-insoluble, non-crosslinked, poly(vinyl alcohol) copolymers which can be hydrated to copolymers having controllably variable hydrogel properties and high strength. Such poly(vinyl alcohol) copolymers are particularly desirable as optical devices such as contact lenses.

This is a division of application Ser. No. 712,353, now U.S. Pat. No.4,694,037, filed 3/15/85, which is a division of application Ser. No.500,785, now U.S. Pat. No. 4,528,325, filed 6/3/83.

FIELD OF THE INVENTION

This invention relates to non-crosslinked copolymers of poly(vinyltrifluoroacetate) with small amounts of either a vinyl ester or adisubstituted ethylene monomer and to novel copolymers derived therefromby solvolysis. In another aspect, it relates to shaped articles, films,and coatings of both poly(vinyl trifluoroacetate) copolymers andpoly(vinyl alcohol) copolymers, the latter being produced by solvolysisof poly(vinyl trifluoroacetate) copolymers. In a further aspect, itrelates to hydrogel contact lenses formed from the poly(vinyl alcohol)copolymers of the invention.

BACKGROUND OF THE INVENTION

Polymers of vinyl trifluoroacetate and vinyl alcohol are known in theart.

U.S. Pat. No. 2,436,144 discloses copolymers of vinyl trifluoroacetateand olefinic compounds useful as sheet materials for wrapping, forimpregnating and coating materials, and in molding applications. It isnoted that optimum properties are obtained when greater than 50 percentby weight of the polymerizable mixture is vinyl trifluoroacetate. Thepatent claims interpolymers containing 15 to 70 weight percent of vinyltrifluoroacetate. Example VIII discloses the hydrolysis of a vinyltrifluoroacetate homopolymer with sodium ethylate to provide a polymerwhich is soluble in water. No examples of suggestion of solvolysis ofcopolymers of poly(vinyl trifluoroacetate) are disclosed.

Harris, et al., J. Polymer Sci. A-1, 4 665-677 (1966) and Haas, et al.,J. Polymer Sci., 22 991 (1956), disclose the hydrolysis of poly(vinyltrifluoroacetate) homopolymers to poly(vinyl alcohol) homopolymers withsyndiotactic properties (i.e., the stereochemical configurations of thetertiary carbon atoms are regularly alternating). U.S. Pat. Nos.3,220,960 and 3,361,858 teach that contact lenses can be made fromcross-linked poly(vinyl alcohol) homopolymer hydrogels.

Copolymers of vinyl alcohol are known and are reported, e.g., inJapanese Patent No. 78/91,995 and Japanese Patent No. 78/103,092; by L.A. Vol'f, et al., Khim. Volokna, 2, 14 (1979) and by J. Chernikov, etal., Nauchn. Tr., Kuban Gos. Univ., 243, 141 (1977). The latterdiscloses cross-linked graft copolymers of poly(vinyl alcohol) andpoly(acrylic) acid useful as biologically active man-made fibers.

None of the above-mentioned art discloses that non-crosslinkedcopolymers of vinyl trifluoroacetate with less than 5 weight percent ofcertain comonomers can provide, by solvolysis, syndiotactic poly(vinylalcohol) copolymers which surprisingly are insoluble in water andpossess the desirable properties of very strong hydrogels. Further, itis known in the art that when cross-linked poly(vinyl alcohol)homopolymers are to be made into contact lenses they cannot be moldeddue to the infusibility of poly(vinyl alcohol), but they must bemechanically cut or machined into the contact lens shape aftercross-linking or curing, then hydrated to form the hydrogels.

SUMMARY OF THE INVENTION

Briefly, the present invention provides novel, non-crosslinkedcopolymers of vinyl trifluoroacetate (VTA) and up to 5 weight precent ofthe VTA of certain comonomers, such as vinyl esters or disubstitutedethylene monomers. Solvolysis of these copolymers provides novelwater-insoluble, non-crosslinked, poly(vinyl alcohol) copolymers whichcan be hydrated to copolymers having controllably variable hydrogelproperties and high strength. Such poly(vinyl alcohol) copolymers areparticularly desirable as optical devices such as contact lenses.

It has not previously been recognized that copolymers of poly(vinyltrifluoroacetate) could be used as a source of water-insoluble,non-crosslinked copolymers of poly(vinyl alcohol), or that such novelcopolymers would give high tensile strength and high modulus hydrogelarticles. The process comprises first casting or molding the poly(vinyltrifluoroacetate) copolymer into articles such as contact lens shapedarticles in the presence of heat (i.e., thermoforming), which process isdisclosed in assignee's copending patent application, U.S. Ser. No.019,068, filed the same date as this application, then solvolyzing theseshaped article copolymers to provide shaped articles of poly(vinylalcohol) copolymers which can be hydrated to provide controllablyvariable hydrogel properties and high strength. This process isparticularly advantageous for the purpose of providing surprisinglystrong contact lenses. Other articles, films, contact lens buttons,sheets and the like which have hydrogel properties, structuralstability, and high strength can also be manufactured using thisprocess.

As used in the present application:

"solvolysis" means the reaction of an ester group capable of cleavinginto a carboxyl-containing compound (e.g., amide, ester, or acid) and analcohol in the presence of a nucleophile such as water (at roomtemperature), ammonium hydroxide or an organic amine or in the presenceof a lower (C₁ to C₄) alkanol (at temperatures up to 60° C.) in one houror less;

"thermoformable (thermoprocessable) polymer" means a polymer which maybe heated to a temperature in the range of 150° to 300° C., andpreferably at about 200° C., and most preferably from 10° to 20° C.above the crystalline melting point (T_(m)) of the poly(vinyltrifluoroacetate) copolymer, maintained at that temperature for 5 sec.to 15 min. and then cooled to provide a shaped article of the polymerwhich will retain its shape under ambient conditions;

"ambient conditions" means room temperature and pressure;

"hydrogel" means a material which absorbs water in the range of 10 to 95percent by weight, without itself dissolving;

"high tensile strength" means having a tensile strength greater than 6.9kg/cm² (100 psi); and

"contact lens button" means a cylindrical-shaped article which ismachinable into a contact lens.

DETAILED DESCRIPTION

The present invention provides a copolymer comprising thenon-crosslinked reaction product of:

(1) at least 95 weight percent, preferably 95 to 99.99 weight percent,of vinyl trifluoroacetate monomer, and

(2) at least 0.01 weight percent, preferably 0.01 to 5 weight percent,of a comonomer selected from vinyl esters and disubstituted ethylenes.

Copolymers of the present invention are prepared by copolymerizing smallamounts of selected comonomers with vinyl trifluoroacetate. The amountsof comonomer used will depend to a certain extent on the comonomerchosen, but will generally be less than about 5 percent by weight of thevinyl trifluroroacetate. The amount of comonomer will also depend uponwhich properties of the polymer and the hydroyzed polymer optionallyderived therefrom ase chosen to be maximized.

The comonomer selected will desirably have a reactivity similar to thatof vinyl trifluoroacetate in order to obtain relatively uniformcopolymerization. Any comonomer chosen preferably polymerizes at a ratecomparable to vinyl trifluoroacetate, although polymerization rates fromone-half to twice as fast are acceptable. For this reason, other vinylesters having up to 6 carbon atoms in the alcohol portion of the ester,such as vinyl acetate, vinyl perfluoro-n-butyrate, vinyl formate and thelike, are useful. Vinyl ethers having up to 8 carbon atoms, such asvinyl tertiary-butyl ether may also be used. Another class of comonomerswhich are particularly useful are disubstituted ethylenes, e.g., estersor anhydrides of lower alkyl (C₁ to C₄)-substituted or unsubstituteddicarboxylic acids having up to 8 carbon atoms, such as derivatives ofmaleic, fumaric, itaconic and citraconic acid, e.g., maleic anhydride,dimethyl itaconate, monoethyl fumarate, and the like. Preferredcomonomers are maleic anhydride and vinyl acetate. They have theadvantages of ready availability and relatively good solubility in vinyltrifluoroacetate monomer as well as good copolymerizability.

The process of the preparation of copolymers of vinyl trifluoroacetateis preferably a bulk polymerization process carried out in aconventional manner induced, for example, by relatively mild heating orirradiation in the presence of a free-radical initiator in a relativelyinert atmosphere, e.g., in a sealed ampoule or other container afterdegassing.

Included among free-radical initiators are the conventional thermallyactivated initiators such as organic peroxides, hydroperoxides, and azocompounds. Representative examples of such initiators include benzoylperoxide, tertiary-butyl perbenzoate, diisopropyl peroxydicarbonate,cumene hydroperoxide, azobis(isobutyronitrile), methyl tricaprylammonium persulfate, and diacyl peroxides such as decanoyl peroxide andthe like. Generally, from about 0.05 to 5 percent by weight of a thermalinitiator is used. These thermally activated initiators are preferred.

Photoinitiators may also be employed to initiate polymerization. Suchinitiators are well known and have been described, for example, inpolymerization art, e.g., Chapter II of "Photochemistry" by Calvert andPitts, John Wiley and Sons (1966). The preferred initiators arephotoinitiators which facilitate polymerization when the composition isirradiated. Representative examples of such initiators include acyloinand derivatives thereof, such as benzoin, benzoin methyl ether, benzoinethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, andα-methylbenzoin; diketones such as benzil and diacetyl, etc.; ketonessuch as acetophenone, α,α,α-trichloroacetophenone,α,α,α-tribromoacetophenone, α,α-diethoxyacetophenone (DEAP),2-hydroxy-2-methyl-1-phenyl-1-propanone,o-nitro-α,α,α-tribromoacetophenone, benzophenone andp,p'-tetramethyldiaminobenzophenone; α-acyloxime esters such asbenzil-(O-ethoxycarbonyl)-α-monoxime; ketone/amine combinations such asbenzophenone/N-methyldiethanolamine, benzophenone/tributylamine, andbenzophenone/Michler's ketone; and benzilketals such asbenzildiethylketal and 2,5-dichlorobenzildimethylketal. Normally, thephotoinitiator is used in amounts ranging from about 0.01 to 5 percentby weight of the total monomeric composition. When the quantity is lessthan 0.01 percent by weight, the photopolymerization rate becomesextremely slow. If the photoinitiator is used in excess of 5 percent byweight, no correspondingly improved effect is observed. Preferably,about 0.05 to 1.0 percent of photoinitiator is used in the polymerizablecompositions.

When the activating energy is ultraviolet light, the irradiation istypically carried out at a temperature of about 0° to 50° C. for 30seconds to 5 hours or more. Following ultraviolet irradiation, thecomposition may be heated at 50° to 100° C. to complete thepolymerization, provided the free-radical initiator is thermallyactivatable.

Heating to effect polymerization is generally at 20° to 100° C., andpreferably at 30° to 70° C. The precise temperature range dependssomewhat on the temperature necessary to activate the free-radicalinitiator. For example, when azobisisobutyronitrile is used as theinitiator the temperature is preferably about 45° to 50° C.

The actual polymerization reaction may be run by combining the vinyltrifluoroacetate, the comonomer and the initiator in a glass ampoule,freezing the reactants with a cold bath such as liquid nitrogen,degassing the ampoule by use of vacuum, and then sealing it. Heating theampoule, e.g., in a constant temperature bath provides the heatnecessary for the initiation of the polymerization reaction. Irradiationgenerally uses an ultraviolet lamp.

The reaction time is generally several hours, and has conveniently beencarried out overnight, i.e., for about 12 to 20 hours, to provideessentially complete conversion of the monomers to copolymers.

Vinyl trifluoroacetate is preferably purified i.e., trace amounts ofacetaldehyde, trifluoroacetic anhydride and trifluoroacetic acid areremoved from the vinyl trifluoroacetate for best results. The copolymerproduct is a white to off-white solid which is soluble inN,N-dimethylformamide, ethyl acetate, acetonitrile, warm acetone, andthe like. Differential thermal analyses show glass transitiontemperatures of about 50° to 100° C. and crystalline melt transitions ofabout 150° to 200° C.

Molecular weights of the poly(vinyl trifluoroacetate) copolymers aretypically greater than 200,000, and preferably in the range of 400,000to 4,000,000, for the weight average molecular weight; such highmolecular weights are preferred since approximately 2/3 of the polymermass is lost in the subsequent solvolysis step which provides poly(vinylalcohol) copolymers. Molecular weights of the corresponding poly(vinylalcohol) copolymers obtained through solvolysis are about 1/3 of thevalue for poly(vinyl trifluoroacetate) copolymers due to loss of mass ofthe trifluoroacetate groups from the poly(vinyl trifluoroacetate)copolymer. In the present invention the molecular weights of thepreferred embodiments generally are characterized by having apolydispersity (P) of less than 2.0. THis indicates a relatively narrowmolecular weight distribution. P is a generally recognized measurementof the overall sharpness or breadth of the range of the molecularweights of polymer chains and is equal to ##EQU1##

Solvolysis of the trifluoroacetyl group of the above-describedpoly(vinyl trifluoroacetate) copolymers provides novel poly(vinylalcohol) copolymers. It is indeed surprising that the poly(vinylalcohol) copolymers of the present invention have greatly improvedhydrogel properties when compared to known hydrogels of comparable waterabsorption capacity. In particular, it has been observed that very smallamounts of comonomer, typically less than 5 percent, provide two or moretimes the weight of water absorption than the homopolymer does. Thisincreased water absorption is particularly important in the preparationof contact lenses, since increased water absorption is known tocorrelate well with increased oxygen permeability, a property essentialto extended wear of contact lenses. As little as 0.25 percent of maleicanydride in a copolymer was observed to more than double the oxygenpermeability of a contact lens prepared according to the presentinvention. Similarly, only 0.5 percent of maleic anhydride in acopolymer was found to increase the oxygen permeability of a contactlens about four times, and with one percent the increase was about 5.5times. After solvolysis, the poly(vinyl alcohol) copolymers of theinvention comprise 85 to 99.97 weight percent of vinyl alcohol monomerunits and 0.03 to 15 weight percent of comonomer units derived fromvinyl esters and disubstituted ethylenes.

Solvolysis is typically carried out under relatively mild conditions,for example, using methanolic ammonium hydroxide at approximately 20° C.The base used is preferably a mild base, including (in addition toammonium hydroxide) the organic amines such as piperidine, morpholine,ethylamine, di(n-propyl)amine, and di(n-butyl)amine, in a diluent. Thebase chosen may influence the ionic character of the polymer. Thediluent used is preferably a non-aqueous liquid which will not dissolveeither the poly(vinyl trifluoroacetate) copolymer or the copolymericpoly(vinyl alcohol) solvolysis product. The diluent can be a loweralkanol (C₁ to C₄) or an ether such as tetrahydrofuran or diethyl ether.The solvolysis is preferably complete, and it is very rapid. Forexample, using 9:1 methanol:ammonium hydroxide as the solvolysisreagent, solvolysis is essentially complete in 15 minutes. The reactiontime may be monitored analytically, e.g., chromatographically todetermine both the rate and the completion of the solvolysis.

Although amounts of comonomer up to 5 percent of the vinyltrifluoroacetate copolymers can be used for some purposes to providedesirable copolymers, the amount of comonomer must be carefully selectedin order to provide good contact lenses. The amount of comonomer will beless than about 5 weight percent in general, but in order to formcontact lenses with maleic anhydride as the comonomer, it has been foundthat an amount in the range of 0.01 to 2 weight percent is preferred,and 0.01 to 1 weight percent is most preferred. Copolymers with lessthan 1 percent maleic anhydride appear to provide, after solvolysis,hydrogel copolymers having high strength, excellent oxygen permeabilityand good optical clarity. Copolymers with greater than 1 weight percentmaleic anhydride become increasingly hazy.

Copolymers which have been solvolyzed and which contain maleic anhydrideas the comonomer contain solvolyzed anhydride units. For example, whenammonium hydroxide is used for solvolysis, the solvolyzed comonomer unitbecomes: ##STR1## For this reason, the copolymers are very slightlycharged at pH 7.

Copolymers with non-solvolyzable comonomer units (e.g., dimethylitaconate), units much less readily solvolyzed than anhydrides (such asvinyl acetate), or with units (such as vinyl esters) which would notsolvolyze to ionic reaction products under the conditions used in thepresent invention would, of course, yield hydrogels with no associatedionic charge. This characteristic (i.e., no ionic charge) has been foundto be of great utility in preparing hydrogel articles with low tendencyto absorb proteins from biological fluids such as the tear fluids of theeye.

Although it is clear that strength is a desirable characteristic ofshaped polymeric articles of the present invention, it also has beenfound that various copolymers will maximize various aspects of strengthto allow selection of different copolymers of the invention for varyingapplications. That is, the copolymer with a good tensile strength andmodulus but less ideal elongation might be preferred under bendingstress in applications such as contact lenses. For applications where apulling stress will be applied to the article, such as vascular grafts,a combination of all three properties is desirable.

The tensile strength, elongation and modulus are all measurements of therelative mechanical properties of a material. Samples of shapedpolymeric articles of both poly(vinyl trifluoroacetate) copolymers andpoly(vinyl alcohol) copolymers of the present invention were evaluatedusing fully hydrated samples at ambient (i.e,. room, e.g., 20° C.)temperature. Tensile strength testing was done in accordance with ASTMD412-80. A commercially available tensile tester (MTS Tensile Tester,MTS Inc., Minneapolis, MN) which was modified to accept sample ringsrather than strips was used. The rings were held over pegs on a sampleholder rather than in conventional jaws, with the object of avoidingsample slippage. Measurements were carried out with samples immersed inwater to prevent drying of the samples during testing. It was found thattensile strengths of 6.9 kg/cm² and greater were obtained. Preferredmaterials exhibited tensile strengths of greater than 13.8 kg/cm² andmost preferred materials had tensile strengths of greater than 20.7kg/cm². By way of comparison hydrogel materials suitable for use ascontact lens materials because of high water content typically havetensile strengths of 0.7 kg/cm² or less. Measuring another aspect ofstrength, the percent elongation before breaking of samples made fromthe polymers and copolymers was determined. Preferred materials showedelongation of at least 70 percent, and most preferred materials showedelongation over 150 percent. As noted in TABLE V below, a commerciallyavailable contact lens had elongation of 110 percent.

Another aspect of strength, the modulus of elasticity, was alsomeasured. The preferred materials of the invention showed a modulus ofgreater than 6.9 kg/cm². Most preferred materials showed a modulusgreater than 10.4 kg/cm². As noted in TABLE V below, a commerciallyavailable contact lens exhibited a modulus of elasticity of 3.2 kg/cm².

Surprisingly, polymer hydrogels of poly(vinyl alcohol) copolymersprepared by the process of the present invention show two distinctimprovements over related materials previously known. The strength ofthese hydrogels of the invention is much greater than that of known,conventional poly(vinyl alcohol) materials such as commerciallyavailable poly(vinyl alcohol) derived from poly(vinyl acetate) byalkaline hydrolysis. When films of the poly(vinyl alcohol) copolymers ofthe present invention are compared to films of commercially availablepoly(vinyl alcohol) in stress-strain measurements, the total energies tofailure, i.e., the areas under the stress-strain curves show distinctdifferences between the polymer films. Over twice as much energy isrequired to cause failure of the poly(vinyl alcohol) copolymer films ofthe present invention. It is hypothesized that this difference inmechanical strength is related to differing intermolecular forcesassociated with the more highly syndiotactic stereochemical structure(i.e., the stereochemical configurations of the tertiary carbon atomsare regularly alternating) associated with the polymers of theinvention. Commercially available poly(vinyl alcohol) has a more atacticstructure (tertiary carbon atoms possessing a random stereochemicalconfiguration) and its crystallinity properties are distinctly differenti.e., the poly(vinyl alcohol) of the prior art has a lower crystallinemelting temperature than the poly(vinyl alcohol) copolymers of thepresent invention.

A second major improvement is in the hydrogel properties of thepolymers. Commercially available poly(vinyl alcohol) derived frompoly(vinyl acetate) generally displays water absorption levels of about40 weight percent or less, depending on drying time and temperature ofthe polymer film used for hydration. Poly(vinyl alcohol) copolymers ofthe present invention, and especially copolymers of poly(vinyl alcohol)containing as little as 1 percent or less by weight of variouscomonomers have water absorption values which may be controllably variedto give hydrogels which absorb much more water than these commerciallyavailable poly(vinyl alcohol) materials. Aqueous liquid absorption(e.g., swelled in water or normal saline) levels of 10 to 90, andpreferably 60 to 70 or more weight percent, are obtained with polymersof the present invention. It is believed that ionic comonomers can leadto enhanced aqueous liquid absorption by affecting the crystallinity ofthe poly(vinyl alcohol) copolymer and by increasing the inherentabsorptivity of the amorphous regions of the polymers. Non-ioniccomonomers may exert their surprisingly large effects principally byaffecting polymer crystallinity.

In order to provide shaped articles of the invention having goodstructural stability, the solid poly(vinyl trifluoroacetate) copolymers(either in the form of the cast films or as solid polymer granules orpowders) are placed in molds of various desired shapes, e.g., contactlens molds or pressed into sheets or films of various shapes. Thepolymer-filled molds of various shapes are then heated, generallyslightly above (i.e., 10° to 20° C. above) the melting point of thecopolymer for 5 seconds to 15 minutes to thermoform the copolymersample. Using this technique, shaped contact lenses and films, contactlens buttons, sheets and articles of various shapes can be obtained.Good retention of shape is observed if the molded poly(vinyltrifluoroacetate) copolymers are solvolyzed to poly(vinyl alcohol)copolymers. If the poly(vinyl alcohol) copolymers are then hydrated toform hydrogels, it is observed that the hydrogel articles retain theirshape under normal room conditions of temperature and pressure andindeed have excellent and improved strength compared to alternativematerials. Corneal implant lenses can also be molded or shaped from thecopolymers of the invention. Solvent solutions may be used to formarticles such as tubes by film coating onn a suitable rod or mandrel.

Articles of the invention may be prepared by any type of molding,casting, vacuum forming, or extrusion process known in the art. Forexample, hydrogel films or sheets of these copolymers can be prepared bysolvent casting a sample of dissolved polymer into a thin film, dryingto evaporate the solvent, treating the film for a relatively short timewith a solvolysis reagent and then placing the sample in water. Theproduct is the desired hydrogel of poly(vinyl alcohol) copolymer. Whilevarious solvents for solvent casting may be used, solvents such asacetone, ethyl acetate or acetonitrile are preferred since theirrelatively high volatility permits an essentially complete removal fromcast films.

Injection molding is an alternative method of molding which is useful toprepare shaped articles from the copolymers of the present invention.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

EXAMPLE 1

A mixture of 5 g of vinyl trifluoroacetate, 0.030 g of maleic anhydrideand 0.025 g of azobisisobutyronitrile was placed in an ampoule, thecontents of which were then frozen with liquid nitrogen. The ampoule wasthen degassed under a vacuum and sealed. The ampoule was heater in abath at about 47° C. for about 16 hours. The contents of the ampoulewere found to be white solid poly(vinyl trifluoroacetate-maleicanhydride) copolymer. The nuclear magnetic resonance spectrum of thecopolymer was consistent with the assigned structure.

EXAMPLE 2

One gram of the product of EXAMPLE 1 was pressed between two polyestersheets at 191° C. for about 45 seconds. After cooling the polymer filmwas placed in a flask and about 20 ml of 10 weight percent concentratedammonium hydroxide in methanol was added. After standing for 15 minutes,the polymer was separated by decanting the liquids, then dried in air toprovide a copolymer of vinyl alcohol and maleic anhydride solvolyzed byammonium hydroxide. The copolymer was found to form a hydrogel whenwater was added. Water absorption provided a clear, strong elastic filmwithout dissolving the polymer sample.

EXAMPLE 3

Using the method of EXAMPLE 1, vinyl trifluoroacetate was copolymerized(99/1 weight ratio) with various monomers to provide the copolymersshown in TABLE I:

                  TABLE I                                                         ______________________________________                                        Sample   Comonomer        Copolymer                                           ______________________________________                                        a        dimethyl itaconate                                                                             poly(vinyl trifluoro-                                                         acetate-co-dimethyl                                                           itaconate)                                          b        monoethyl fumarate                                                                             poly(vinyl trifluoro-                                                         acetate-co-monoethyl                                                          fumarate)                                           c        vinyl perfluorobutyrate                                                                        poly(vinyl trifluoro-                                                         acetate-co-vinyl                                                              perfluorobutyrate)                                  ______________________________________                                    

Using the method of EXAMPLE 2, the copolymers of the above examples werethermoformed, then solvolyzed to provide the copolymers of TABLE II:

                  TABLE II                                                        ______________________________________                                                                            Water                                                                         sorption*                                       Copolymeric   Copolymeric     (weight                                   Sample                                                                              starting material                                                                           product         percent)                                  ______________________________________                                        a     poly(vinyl trifluoro-                                                                       poly(vinyl alcohol-co-                                                                        47                                              acetate-co-dimethyl                                                                         dimethyl itaconate)                                             itaconate)                                                              b     poly(vinyl trifluoro-                                                                       poly(vinyl alcohol-co-                                                                        58                                              acetate-co-monoethyl                                                                        monoethyl fumarate)                                             fumarate)                                                               c     poly(vinyl trifluoro-                                                                       poly(vinyl alcohol-co-                                                                        42                                              acetate-co-vinyl                                                                            vinyl perfluorobutyate                                          perfluorobutyrate)                                                      ______________________________________                                         *The water sorption of the polymers (percent H.sub.2 O) of Tables II, III     and IV was a weight percent determination using the formula                   percent H.sub.2 O = [(W.sub.2 - W.sub.1)/W.sub.2 ] × 100                where W.sub.2 is a waterswollen sample weight and W.sub.1 is dry sample       weight.                                                                  

EXAMPLE 4

A mixture of 50 g vinyl trifluoroacetate, 0.75 g vinyl acetate and 0.25g of decanoyl peroxide was placed in an ampoule. The ampoule was sealedand maintained at 47° C. for about 16 hours, then at 57° C. for twohours. The product, poly(vinyl trifluoroacetate-polyvinylacetate)copolymer, was removed from the ampoule, pressed into sheets andsolvolyzed by treating with 10 percent ammonium hydroxide in methanol.The product was poly(vinyl alcohol-polyvinyl acetate) copolymer asconfirmed by nmr spectroscopy.

EXAMPLE 5

A mixture of 50 g vinyl trifluoroacetate, 0.75 g vinyl acetate, and 0.05g 2-hydroxy-2-methyl-1-phenyl-1-propanone was placed in an ampoule. Theampoule was sealed and then rotated under a ultraviolet sunlamp forabout three hours. Air was blown over the ampoule during the irradiationto cool it. The product, poly(vinyltrifluoroacetate-polyvinyl acetate)copolymer, was removed from the ampoule and pressed into sheets at 191°C. for two minutes. The sheets were solvolyzed in 10 percent ammoniumhydroxide in methanol for thirty minutes to provide poly(vinylalcohol-polyvinyl acetate) copolymer.

EXAMPLE 6

The poly(vinyl alcohol-polyvinyl acetate) copolymers (each containing1.5 percent by weight (calculated) polyvinyl acetate) from EXAMPLE 4 and5 were evaluated for various properties. The results are shown in TABLEIII below:

                                      TABLE III                                   __________________________________________________________________________                Oxygen                                                                            Tensile   Elonga-                                                                            Protein bound                                         Weight                                                                             perme-                                                                            strength                                                                           Modulus                                                                            tion (micrograms/cm.sup.2)                          Sample % water                                                                            ability*                                                                          (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      %    albumin/globulin/lysozyme                      __________________________________________________________________________    a      66   32  50   7.2  620  2.4  0.4 4.8                                   (thermally                                                                    polymerized)                                                                  b      69   26  55   6.9  515  0.5  0.25                                                                              2.4                                   (UV                                                                           polymerized)                                                                  __________________________________________________________________________     *gas phase oxygen permeability                                           

The data of TABLE III show the excellent physical properties of thepoly(vinyl alcohol) copolymers of the invention.

EXAMPLE 7

In order to compare the effect of varying levels of vinyl acetatecomonomer, the following general procedure was followed to prepare fourcopolymers. Vinyl trifluoroacetate and vinyl acetate, quantities asindicated in TABLE V below, and 0.05 g of decanoyl peroxide were sealedin ampoules and maintained at 47° C. for sixteen hours. The polymer wasremoved from each ampoule and pressed into sheets at 191° C. for abouttwo minutes. Each sample was solvolyzed in 10 percent ammonium hydroxidein methanol for thirty minutes, dried and weighed dry, then allowed toabsorb water and weighed to determine the percent water absorbed asshown below:

                  TABLE IV                                                        ______________________________________                                              Vinyl                                                                   Sample                                                                              trifluoroacetate                                                                           Vinyl acetate                                                                             Water absorbed                                 no.   (g)          (g)         (weight percent)                               ______________________________________                                        a     9.9          0.05        42                                             b     9.875        0.075       57                                             c     9.85         0.10        68                                             d     9.82         0.13        69                                             ______________________________________                                    

The data of TABLE IV show that very small amounts of comonomerssignificantly improve the water absorption of poly(vinyl alcohol)copolymers.

EXAMPLE 8

A mixture of 50 g of vinyltrifluoroacetate, 0.75 g of vinyl acetate and0.05 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was placed in areactor and covered with a layer of 500 ml of ice-water. The reactor wasirradiated under an ultraviolet sunlamp for 3 hours. The productcopolymer was separated, rinsed with methanol and dried. The copolymerwas then melt-processed according to the procedure of EXAMPLE 2 intofilm samples and solvolyzed in 10 percent ammonium hydroxide in methanolfor 30 minutes to provide poly(vinyl alcohol-co-vinyl acetate) filmswhich when swollen in water gave transparent high strength hydrogelmaterials.

EXAMPLE 9

Poly(vinyl trifluoroacetate-co-vinyl acetate) from EXAMPLE 8 waspurified by dissolving the polymeric product in acetone to provide a 25percent by weight solution, followed by precipitation into heptane (anon-solvent for the polymer) resulting in the formation of fibrouspolymer. This polymer was dried, then thermally processed by pressing at191° C. for two minutes into sheets. Thermal stability was measured bystandard thermogravimetric analysis techniques (using a MettlerThermogravimetric Analyzer, Mettler Instruments, Chicago, Ill.),comparing weight loss at various temperatures. These polymer sheetsshowed better thermal stability than sheets which had not been purifiedbefore melt processing.

EXAMPLE 10

TABLE V shows how percent water absorbed, estimated gas phase oxygenpermeability and various measures of strength can be varied by varyingthe amount of comonomer present in copolymer hydrogels derived fromappropriate vinyl trifluoroacetate copolymers prepared according to themethod of EXAMPLE 1 and solvolyzed according to the method of EXAMPLE 2.

                                      TABLE V                                     __________________________________________________________________________    Variation of Properties of Polyvinyl Alcohol-Maleic Anhydride Copolymers                                    Tensile                                             Polymer    Weight percent                                                                        Oxygen strength                                                                           Modulus                                                                            Percent                               Sample                                                                            (% is by weight)                                                                         water absorbed                                                                        permeability                                                                         (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      elongation                            __________________________________________________________________________    a   Polyvinyl alcohol;                                                                       41      5.4    162  115  750                                       0% maleic anhydride                                                       b   Polyvinyl alcohol                                                                        54      12     90   44   680                                       plus 0.25% maleic                                                             anhydride                                                                 c   Polyvinyl alcohol                                                                        65      20     48   23   530                                       plus 0.5% maleic                                                              anhydride                                                                 d   Polyvinyl alcohol                                                                        72      30     26   17   440                                       plus 1.0% maleic                                                              anhydride                                                                 e   Commercially                                                                             55      12     1.6  3.2  110                                       available                                                                     lens                                                                      __________________________________________________________________________     *The opthalmic devices of the present invention preferably exhibit an         oxygen permeability (pO.sub.2) of at least 10 Barrers when measured in        accordance with the polarographic oxygen electrode method described by M.     F. Refojo et al, "Permeability of Dissolved Oxygen Through Contact Lenses     1. Cellulose Acetate Butyrate", Cont. Intraocular Lens Med. J. 3(4), 27       (1977). More preferably the devices of the invention exhibit an oxygen        permeability of at least 20 Barrers.                                          The estimated pO.sub.2 was determined by the method of Refojo referenced      above. The units are 10.sup.-11 ml of O.sub.2 · cm/sec .multidot     cm.sup.2 · mmHg.                                                

EXAMPLE 11

The copolymer of EXAMPLE 10, Sample c, of 99.5 weight percent vinyltrifluoroacetate and 0.5 weight percent maleic anhydride was dissolvedin acetone to give a 20 weight percent solution. The solution was castonto a clear polyester film in sufficient thickness to give, aftersolvent evaporation, a clear film of approximately 0.015 inches (about0.4 mm) thickness. This film was placed in a metal mold designed to forma single contact lens, and the mold (heated at approximately 200° C.)was closed under pressure (hydraulic ram pressure of approximately 1000psi or 70 kg/cm²) for approximately two minutes.

The mold was cooled and the molded lens was removed and placed in acontainer with approximately 20 ml of 9/1 methanol-concentrated ammoniumhydroxide for about 15 minutes. The solvolyzed contact lens was then airdried and placed in distilled water. Hydration provided a clear,flexible, very strong hydrogel lens.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

I claim:
 1. A copolymer comprising the non-crosslinked reaction productof:a. at least 95 weight percent of vinyl trifluoroacetate monomer, andb. at least 0.01 weight percent of a comonomer selected from vinylesters, vinyl ethers, and copolymerizable disubstituted ethylenes.
 2. Acopolymer according to claim 1 wherein said comonomer is selected frommaleic anhydride, vinyl acetate, dimethyl itaconate, monomethyl fumarateand vinyl perfluorobutyrate.
 3. A copolymer according to claim 1 whereinsaid comonomer is maleic anydride.
 4. A copolymer according to claim 3wherein said comonomer is present in an amount in the range of 0.01 to 2weight percent.
 5. A copolymer according to claim 1 derived from vinyltrifluoroacetate and vinyl acetate.
 6. A copolymer according to claim 1wherein said comonomer is present in an amount in the range of 0.01 to 5weight percent.
 7. A shaped article comprising a copolymer according toclaim
 1. 8. The shaped article according to claim 7 which is a contactlens.
 9. The copolymer according to claim 1 wherein said vinyl ethercontains up to 8 carbon atoms.